I have run a very simple file, print, backup and SVN server at home for a number of years. It was built using old parts laying about the house. A few weeks back the fan on the video card and the chipset fan on the motherboard died. I had another old AGP video card so I slapped that in and it kept running until this past Thursday.
My wife needed data off the HD so I had here take the external USB drive I use for Monday / Wednesday / Friday backup cycle and had her plug it directly into her machine. Made me a bit nervous but she needed her files. I just asked her not to delete anything.
Thursday night I pieced together a new machine to be the server. I plugged in the original HD and went to work. This was my son's box and it had been acting flaky so I had some doubts. I got WinXP running again but when I tried to the the motherboard USB 2.0 drivers to work things went to hell quickly. Devices were not recognized and unplugging or plugging one in could cause a BSOD and reboot.
I spent way too many hours on this before I gave up. I hit the web to see what the cheapest Win7 based machine I could get at Microcenter happened to be. I was sick of WinXP on the server and all other machines in the house are running Win7. They had an open box eMachine for $215. I know, it is an eMachine but I have bought them in the past for family members on budgets and if you just run what it has as the base configuration they keep running. I have not had one fail yet. My big worry is their small power supplies.
This is a typical machine with AMD 2.8g processor, 2g of RAM, 500 mb HD, nVidia chipset and video card in a slim line case with plenty of USB 2.0 ports. Fired right up and I spent the next bunch of hours uninstalling crap, installing patches and restoring a previous backup from the external USB drive. The proper area of the drive is shared and the printer is shared so the rest of the family is happy. I have installed Apache and SVN but have not fully configured them yet. I was sick of computer stuff so I played some games and did work on a side Android project.
In the end of should have given up much earlier and just bought a new machine. Trying to get old suspect hardware running just to be cheap is not a good solution. We have proven over the years that the server is critical to running our house. I have plans to get more services running on the box - SVN, some flavor of SQL, etc. so it needs to be slightly on the mission critical side of things.